I wouldn't say js runs everywhere... If you're getting started out it's possible they might use shared hosting instead of roll a VPS..so while js/jquery will work everywhere... NODE/JS as a backend won't unless nodejs is installed.

However PHP + Jquery is a good option and it DOES literally work everywhere.. I've run laravel from shared hosting... wanted to kill myself and can't run everything like using a redis cache...

You can also use laravel for backend, frontend, and mobile (as an api). A good mix is laravel api + cordova or ionicframework for the mobile part.